One such arrangement is described in patent document U.S. Pat. No. 7,068,404.
That document describes a thin light guide using a hologram and a prismatic lens serving to magnify the size of the miniature screen and project a virtual image thereof in front of the wearer's eye.
Another type of prior art arrangement is described in patent document EP 1 566 682.
That document describes a beam-expanding light guide that is even thinner than that of the preceding prior art, and it likewise describes an optical system capable of projecting the image of a miniature screen to infinity.
The common point of those systems is that the major part of the optical power for magnifying the image of the miniature screen is located outside the light guide. In those arrangements, fields of view of the order of 15° to more than 30° can be achieved, while retaining light guide thicknesses that are small.
Nevertheless, in order to obtain such fields of view of more than 20°, present arrangements include optical systems and miniature screens that are of relatively large volume given that since the size of the miniature screen is an important factor in dimensioning the size of the associated optical systems. The opto-mechanical assembly that is needed is found to be too large compared with the waveguide thickness that it is desired to make as small and fine as possible, so as to enable it to be incorporated in an ophthalmic lens, for example.
Patent document US 2001/0048554 discloses an electronic display arrangement for taking light signals forming an image emitted from a miniature screen and, referred to as a screen image, and for conveying them towards the eye of a user to enable a virtual image to be viewed.
That arrangement includes a miniature screen control device having an arrangement for subdividing a source image into two screen images, and a mosaicing device having an exit viewport and serving to convey the screen images in a manner in which they are spatially offset from each other and time shifted from each other, at a period of less than 25 milliseconds (ms).
Each screen image is conveyed towards the eye of the wearer so as to enable a virtual sub-image to be viewed, the two resulting and adjacent virtual sub-images together forming said virtual image in full.